When installing carpets, a carpet trimming tool is used to trim excess carpet from the edge of a section of carpet. This edge is trimmed at a location of the carpet along the wall of a room. Typically the excess carpet along the wall is folded up the wall when the carpet is just about to be trimmed. Ideally the carpet trimming tool can make a precision cut to trim close to a wall, while also cutting the carpet slightly larger than the room such that an edge of the carpet may be tucked into a narrow gap between the tack strip and the wall. As the slight excess of carpet that is desired for tucking is located at a point which is lapped up the wall, the carpet trimming tool requires its blades to be held at an elevation slightly higher than the face of the carpet. Such a tool may move along the edge of the room cutting a length of carpet slightly longer than the edge of the room. In addition the tool should have blades that can be adjusted to accommodate both the type of carpet and the features of the room.
A typical carpet trimming tool includes a base, a handle mounted on the base, a blade holder, and a means for adjusting the tool. Typically such carpet trimming tools may be adjusted in two dimensions. The blade holder may be adjusted such that the blades are at varying heights with relation to the base. This adjusts the amount of carpet which is trimmed allowing more or less carpet to be left to tuck between the gap between a tack strip and a wall. Secondly, the spacing between the outer edge of the base of the trimmer and a guide which contacts the wall (called a wall runner), which defines the carpet entry space or “throat” must be adjustable for various thicknesses of carpet.
All references in this section are hereby expressly incorporated by reference herein.
One prior art carpet trimmer is illustrated in U.S. Pat. No. 2,772,474 (the '474 device). This reference discloses a carpet trimmer including a substantially flat base on which two posts are mounted. A stack of spacers may be secured over the posts. A blade holder is inserted between two spacers. The blade holder is typically an “L” shaped metal part, having a first long surface which acts as the blade holding surface. The blade holder is designed to be mounted between spacers. A second, shorter surface is formed by a downward bend and contacts the wall to guide the trimmer (hereinafter the “wall runner”). The blade holder surface has a set of parallel slots. The posts on the base run through these slots as the user inserts the blade holder into the shim deck. The posts on the base may retain the slots as a user slides the blade holder past the post. Once the blade holder is inserted between two spacers, a fastener (such as a bolt) may be tightened down on top of the spacer stack, frictionally holding the blade holder at a selected height. The more spacers underneath the blade holder, the more the trimmer will leave of the carpet edge that is folded up against a wall. This allows more carpet that will remain uncut and available for tucking.
Depending upon the type of carpet and the space of the gap between the tack strip and the wall, different amounts of excess carpet are desirable. For this reason, an exact adjustment in height is necessary for a carpet trimming tool. This reference also discloses a means to adjust the throat width. The throat adjustment is necessary in the area where the carpet enters the trimmer. For thick plush carpets, the throat width of the tool must be adjusted such that there is sufficient width to accommodate the thickness of the carpet. In the above-cited reference, a locating plate is used in conjunction with the blade holder to provide a means for throat adjustment. The locating plate includes a number of holes on side edges of the locating plate and a spacer retaining dimples at a back edge of the plate. On the blade holder a pair of side dimples fit into the holes on the locating plate. The plurality of holes spaced along the sides of the locating plate allow adjustment of throat width. On the locating plate are slots, similar to those on the blade holder, which engage the posts mounted on the base. Altering which holes on the locating plate the dimples are secured into changes the width of the blade holder face (wall runner face) from the locating plate. When the two devices are inserted onto the post, the width of the throat is thus changed.
The blades on this device are mounted on the bottom side of the blade holder. A pair of spring clips holds the blades against this bottom side surface. The front end of the blade is held in place by a raised lip formed within the inside surface of the wall runner. The back end of the blade is held in place a raised lip. The locating plate is shaped such that the spring clips are accommodated within a gap on the locating plate.
There are a few drawbacks to the design of this tool. When changing the blades, the location of blade insertion on the bottom side of the blade holder creates many problems. When the blade holder is removed from the shim deck, the user must flip the blade holder upside down to even view the blades, which is awkward from a visual standpoint. The use of biased springs to hold the blades against the underside of the blade holder requires significant force in order to remove the blades. Without great caution, the user is likely to cut his finger. After many blade changes, the biased springs tend to lose their shape and become less effective at holding the blade.
Whenever height adjustment is required, the two-piece combination of blade holder and locating plate is difficult to insert between two shims. The user has to separate the shims with one hand, and insert the blade holder and locating plate with the other hand. Often the dimples on the blade holder slip out of the holes in the locating plate. The shims prevent the user from seeing the relationship of the holes and the dimples. For these reasons, misalignment is a common problem and further adjustment is often required.
To address some of the weakness of this '474 device, new devices have been designed. One is disclosed in U.S. Pat. No. 4,095,341 assigned to Crain Cutter Company, Inc. This device includes a blade holder designed to sit on top of a deck of shims. If a user requires a different height adjustment of the blade holder, one or more shims is removed. Thus, inserting the blade holder between the shims is not necessary.
As with the '474 device, the tool includes a base and a pair of posts mounted on the base. However, to enable a different means of throat adjustment, the base of the device has two parts, a handle retaining plate including two slots, and a false bottom plate onto which the posts are mounted. The handle holding plate has two dimples next to the slots. The false bottom plate has two posts extending from it which may be inserted through the two slots on the handle retaining plate. The false bottom plate also includes several holes adjacent to the posts. These holes may be fitted into the dimples. This configuration allows adjustment of the posts in relation to the front edge of the base, and in turn, moves the entire shim deck and blade holder, which in turn provides the means for throat adjustment. Unlike the '474 device, this means of throat adjustment is a highly visual process. When viewed from the base of the trimmer, the entire process is plainly visible.
Because the blade holder is always positioned on the top of the tool the user has a simplified means of changing the blades. A nut or fastener may be removed from the top of the posts and a blade-retaining bracket removed from on top of the blade. In this way, the blade may be removed from a surface on top of the trimmer, not beneath the shims and blade holder. No biasing spring is required because a bracket secures the blade in place in a blade recess area. This greatly reduces the chances of the user cutting their hand during blade change. This also provides the quickest way of changing the blade given that the height adjustment is not again required after the blade has been changed. In addition, the top mounting allows a precisely defined blade holding pocket to be manufactured into the top surface of the blade holder. This provides a highly rigid and durable blade holding means.
U.S. Pat. No. 6,421,923 (the '923 patent), also to Crain Cutter Company, Inc., is a further refinement of the above reference. In this reference the means of constructing the blade holder allows for a more open throat area with fewer obstructions allowing smoother cutting. In addition the blade holder is simpler to manufacture, reducing the cost of the device. This is done in part by spot-welding onto the inner surface of the wall runner a separate metal stamping acting as the support surface or “lip” to hold up the outer edge of the blade. The cost to spot weld on a separate part, rather than to form a support surface into the wall runner itself by means of secondary stamping operations, proves to substantially reduce production cost.
This reference also discloses the top loading blade holder having a retaining blade cover secured by a fastener onto the bolt, similar to the previous reference. In this reference the blade-holding space on the blade holder is made longer overall so that the blades may be more easily inserted. Once the blade is inserted it is simply slid forward into position. When the blade is slid forward a small gap behind the blade on the blade-holding pocket must be filled to securely hold the blade. For this purpose, detents are stamped into the back edge of the blade retaining bracket. These detents are seated in the open area behind the blade. The detents thus define the back edge of a blade holding area and serve to securely hold the blade. In this manner the blade does not need to be fit within a precisely sized blade-retaining pocket, which may be somewhat cumbersome and possibly risk injury from the blade.
This reference also discloses a novel shape for the front edge of the blade holder. This is the location of the tool that bends downward to form on its outside, a wall runner surface, and on its inside, a blade retaining surface. On its top face, the wall runner has a slight upwards bend which creates a small “rise”. After the rise there is a substantially flat area. Past this flat area there is the steep downward bend required to form the wall runner surface. The “rise” and “flat” are needed in order to provide clearance for the blade to pass across the throat area and rest flat against the blade support on the inner edge of the wall runner. If there were no “rise”, the blade would be met by a curved area formed by the downward bend that creates the wall runner surface. Such a curved area, if located where the blade meets the wall runner, could not provide adequate clearance, with the result that the blade might become angled downward. If the blade is angled downward, it will act as a wedge, causing the tool to be pressed constantly downward. This not only makes the trimming operation inaccurate, but increases the force required to perform it.
This concept of a “rise” followed by a flat area disclosed by the '923 patent also creates a significant labor cost advantage compared to the prior art devices cited heretofore. In the prior art devices the required “rise” was created by a sharp upward bend of the material followed by an immediate downward fold. This folding operation is labor-intensive, and, from a tolerance standpoint, very difficult to control.
As noted in the discussion of prior art references, some means is required for holding the front of the blade on the blade holder within the pocket in which the blade is inserted. The blades used in a carpet trimmer are ground and therefore beveled on only one surface. The beveled surface is meant to face upward when the blade is placed in the trimmer. In operation, the bevel creates a generally downward force. This downward force is counteracted by the blade supporting lip on the inner surface of the wall runner. Thus the upward or downward deflection of the blade is controlled.
In the first two listed references, blade support for the front edge of the blade was formed by secondary stamping operations which create lips on the inner surface of the wall runner. This also added to the difficulty in manufacturing the blade holder to proper position. However in the '923 reference a separate blade-holding support is spot-welded onto the inner surface of the wall runner where the front of the blade rests. This reduces cost of manufacture and greatly speeds up manufacture of the wall runner portion of the tool.
U.S. Pat. Nos. 4,095,341 and 6,421,923 present a number of advantages. However one potential disadvantage is that to adjust the height, one or more spacers is removed from a stack of spacers. Some users have difficulty keeping track of the extra spacers that are not stored on the tool. Thus it is one object of the invention to provide a carpet trimmer that does not require spacers to be taken off of the tool. In addition it is an object of the invention to provide a carpet trimmer that allows visual inspection of the throat width from above.
In addition, it is an object of the invention to provide a faster means of reinserting the blade holder between two shims which does not require a separate locator plate. In addition, it is an object of the invention to provide a means of blade holding on the top side of a blade holder that is designed to be inserted and fastened between two shims.